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Occasional Visitor
Posts: 1
Registered: ‎12-22-2016
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Floating deskew values with DWDM encryption cards

Hi, 

 

Customer is upgrading DWDM hardware and new DWDM has encryption cards. ISLs are configured as 3 x 4Gbs trunks

(Brocade 48k, FICON environment). Everything works well, but each link initialisation gives different deskew value in a wide rage starting from 30, finishing at 203. 

 

Does this may hurt trunk performance? Does Brocade ASIC takes into account deskew values in spreading frames across links in trunk OR is it only a entry level counter, and later on ASIC uses links at full speed regardless of deskew value?

 

Od course, I know recommendations and that big deskew difference influences performance, but this statement assumes difference in fibre lengths and quality. We use the same fible lines and with the old DWDM we have difference up to 20 in deskew values. Now something influences in betweeen and we are starting to blame encryption cards. 

 

TIA, 

Grzesiek

Brocade Moderator
Posts: 216
Registered: ‎03-29-2011

Re: Floating deskew values with DWDM encryption cards

Hi,

 

Deskew values should be within range of 30m (delta) as before to ensure that frames are delivered in order. High deskew value can impact performace. But the ASIC will be running the link at 4GB (full speed), but deskew values will be used to keep IOD.

 

Since deskew based is based on the time it takes to send a frame between switches and if the encryption adds latency, you might very well see increased deskew values. Try to disable enscryption.




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Valued Contributor
Posts: 536
Registered: ‎03-20-2011

Re: Floating deskew values with DWDM encryption cards

I guess that your new DWDM kit uses TDM, and this usually creates high and random desqew between the neighbor links. The manual says you should disable trunking in such scenario.

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